Cyanine compounds have hitherto been known to be used as absorbents for the rays within the near infrared and infrared regions, but the cyanine compounds are generally unstable to light and heat. On the other hand, since naphthalocyanine compounds are extremely stable to light, heat and humidity and excellent in toughness, they attract attention to be used as polymer materials for preparing films or thin membranes having high performance characteristics by blending with various dyes, pigments, optical information recording media, photoelectric conversion media, electron photographic sensors and polymer materials.
However, naphthalocyanine compounds are generally scarcely soluble in organic solvents and thus difficulties are encountered in forming films thereof by ordinary film forming processing. Accordingly, there is an earnest demand for a compound having excellent properties comparable to naphthalocyanine compounds and capable of forming a film, and there is also an earnest demand for the development of a process for preparing such a compound on an industrial scale.
Also already proposed and applied for practical use as optical recording media are recording media each having an inorganic recording film layer made of a low melting point metal such as Te, Te alloys or Bi alloys.
However, production efficiency of such a recording medium having an inorganic recording film layer is low since the recording film layer must be formed by vacuum evaporation, or sputtering and there is a problem in recording density since the thermal conductivity of the recording film layer is high. Furthermore, since a harmful metal is used to prepare a recording medium having such an inorganic recording film layer, it is essential to overcome the problems concerning operation environment and waste water disposal.
In order to solve these problems, various proposals have been made to use phthalocyanine pigments which are known as blue to green pigments and excellent in stability as materials for optical recording media, specific examples being copper phthalocyanine, lead phthalocyanine, titanium phthalocyanine, vanadyl phthalocyanine and tin phthalocyanine (Unexamined Japanese Patent Publication Nos. 36490/1983 and 11292/1984). However, these pigments are inferior in matching with the semiconductor lasers, which are commonly used as the recording lasers at the present day, having oscillation wavelengths at approximately 780 to 830 nm, since they have maximum absorption wavelengths in the vicinity of 700 nm.
Under these circumstances, although there is proposed a process in which the absorption wavelengths are shifted to the long wavelength region by means of processing with organic solvents or heating treatment, such a process has not yet been applied for practical use since these metal phthalocyanine pigments are scarcely soluble in organic solvents, in addition to complicated processing steps, so that it is impossible to form a thin film on a substrate made of a thermoplastic resin substrate, such as polycarbonate by coating solutions thereof and it is inevitable to use vacuum evaporation coating or sputtering technique.
In order to solve various problems described above, an optical recording medium has been proposed, in which a soluble organic pigment is used to form a recording film layer on a substrate by coating. More specifically, developed and applied for practical use is an optical recording medium which is formed by spin coating an organic pigment which has an absorption wavelength within the oscillation wavelengths of semiconductor lasers and is soluble in organic solvents, more specific examples of such a pigment being dithiol-metal complexes, polyamine pigments, squaraine pigments, cyanine pigments and naphthoquinone pigments.
However, the optical recording media containing the aforementioned organic pigments have disadvantages that they are poor in durability and weather-proof properties and low in reflectivity needed for reproducing the informations. Also known in the art as pigments which are excellent in durability and weather-proof properties and have absorption peaks vicinal to 800 nm are naphthalocyanines having the tetraazaporphyrin skeletal structure similar to phthalocyanine pigments (Inorg. Chim. Acta., 44, L209 (1980); Zh. Obshch. Khim., 42(3), 696 (1972)). However, these known naphthalocyanines and metal salts thereof have a disadvantage that they are more scarcely soluble in general organic solvents than the corresponding phthalocyanine compounds.
In recent years, various investigations have been made to improve the solubility of naphthalocyanines and metal salts thereof in organic solvents (Specification of U.S. Pat. No. 4,492,750, Specification of U.S. Pat. No. 4,725,525, Unexamined Japanese Patent Publication No. 25886/1986, J. Am. Chem. Soc., 106, 7404 (1984), Unexamined Japanese Patent Publication No. 177287/1986, Unexamined Japanese Patent Publication No. 177288/1986 and Unexamined Japanese Patent Publication No. 184565/1985), and it has been known that aromatic hydrocarbon solvents and halogenated solvents may be used as the organic solvents for dissolving these compounds. However, since the solubilities of these compounds, for example, in saturated hydrocarbon solvents and alcohol solvents are extremely low, there arises a problem that a layer resisting to solvent must be formed on a polymethyl methacrylate or polycarbonate substrate when a recording film layer is formed on such a substrate.
Further known to improve the general solubilities of naphthalocyanines is a method in which plural substituting groups having long chain alkyl groups are introduced. However, if the solubility is improved by such a method, the melting point of the resultant product is lowered to induce a disadvantage that the recording film layer tends to melt when the optical recording medium is subjected to reproduction for a long time as well as during the recording step. Accordingly, there is a demand for the development of a method for solubilizing the naphthalocyanine compounds in saturated hydrocarbon solvents and alcohol solvents without lowering the melting points thereof.
In general, naphthalocyanines have a disadvantage that the once formed amorphous recording film is crystallized gradually under a high temperature and high humidity condition to lose the recorded information since they have large planar .pi.-conjugated bonds to have extreme association force between individual molecules. Accordingly, there arises a problem that such crystallization must be suppressed.
Accordingly, an object of this invention is to provide a novel derivative of naphthalocyanine containing a perfluoroalkyl group, which is excellent in weatherability, high in solubility in various organic solvents and capable of forming a film, and to provide a process for preparing the same.
Another object of this invention is to provide an industrially useful process for preparing a derivative of naphthalocyanine containing a perfluoroalkyl group at high yield without using any special apparatus and reaction catalyst within a short time.
A further object of this invention is to provide an optical recording medium which has high sensitivity and durability including resistance to reproducing laser beam, resistance to environment and resistance to crystallization.